Chapter 24: Glycogen Dehydration Flashcards
Glycogen is highly ______ homopolymer for only ______ present in all tissues
branched
glucose
Largest stores of glycogen are in
liver and muscle
Function for glycogen in the liver
Glycogen synthesis and degradation maintain glucose levels for the needs of the whole body
Maintains blood glucose concentration
Function for glycogen in the muscle
(Selfish)
Stores glycogen to provide energy just for muscle contraction
Glycogen
Storage form of gluocse in animals (including humans)
Glycogen releases glucose when
low energy (energy demands are high)
breakdown of glycogen to start cellular respiration with free glucose
When does glucose polymerize to form glycogen ?
When organism has no immediate need for energy derived from glucose breakdown –> synthesis of glycogen
Structure of glycogen
highly branched
alpha 1,4 linkages and alpha 1,6 linkages
Why is glycogen being highly branched important?
Makes it possible to store and deliver energy quickly and store for long periods
What must be needed for energy demand for glycogen degradation?
break 2 bonds: alpha 1,4 linkages and alpha 1,6 linkages
Key regulatory enzyme for glycogen degradation
Glycogen phosphorylase
Glycogen phosphorylase
key regulatory enzyme of glycogen degradation
degrades glycogen from nonreducing ends of the glycogen molecule
glycogen catalyzes phosphorylysis to form glucose 6 phosphate
breaks down alpha 1,4 glycosidic compound
What enzyme breaks down alpha 1,4 glycosidic bond from nonreducing sugars?
Glycogen phosphorylase
Does glycogen phosphorylase use phosphorlysis or hydrolysis
Phosphorylysis
Phosphoglucomutase
converts glucose 1 phosphate to glucose 6 phosphate
(use of glucose 1,6 biphosphate intermediate)
Transferase
transfer branch of 3 glucose residues to end of another branch
Debranching enzymes (alpha 1,6 glucosidase)
Cleaves alpha 1,6 glycosidic bond at branch point to release free glucose
Where is the only location of gluocse 6 phosphatase?
Liver
(NOT IN THE MUSCLE!)
Liver glycogen breaks down to
glucose 6 phosphate with hydrolysis
Glucose 6 phosphatase
gluocse 6 phosphatase in liver generates free glucose to enter blood and be used in different tissues
Muscle glycogen breaks down
glucose 6 phosphate btained from glycogen breakdown enters glycoltic pathway directly
Does not have to be hydrolyzed to glucose and exported to blood stream
Does glucose 6 phosphatase located in the muscle?
No
Why is it advantageous that breakdown of glycogen gives rise to glucose phosphate to glucose?
Save 1 ATP that is used from glucose to gluocse 6 phosphate
So when we start from glucose 6 phosphate, it is able to generate an additional ATP
After you eat a meal, does degradation of glycogen or synthesis of glycogen occur?
Synthesis of glycogen
Regulation of synthesis and degradation of glycogen
reciprocally regulated: 1 activated and 1 inhibited
Step 1 of glycogen synthesis
Glucose 1 phosphate react with UTP to generate UDP glucose (UDPG)
releases 2 phosphate
UTP glucose
monomer used to extend glycogen chain in synthesis
When adding UDP to gluocse, it is added to
growing chain
Step 2 of glycogen synthesis
Uses glycogen synthase
catalyze formation of alpha 1,4 glycosidic bond using UDP glucose on growing chain
What is key regulatory enzyme of glycogen synthesis?
glycogen synthase
Glycogen synthase
key regulatory enzyme of glycogen synthesis
catalyze formation of alpha 1,4 bond using UDPG on growing chain
What is the primer of glycogen synthesis?
Glycogenin
Step 3 of glycogen synthesis
Branching enzymes
Cleaves alpha 1,4 linkage and transfers 7 glucose residues to form alpha 1,6 linkage
Glycogen is _____ storage of glucose
efficient
How much ATP required to incoporate dierty glucose into glucogen
2 ATP
Complete oxidation of gluocse derived from glycogen yields:
31 ATP
Glycogen phosphorylase interconvertable forms:
- active phosphorylated phosphorylase a
- inactive unphosphorylated phosphorylase b form
Default state of liver phosphorylase is:
active phosphorylated phosphorylase a form
The 2 forms of phosphorylase a and b exist in equilibrium:
- active relaxed R state
- less active T state
equilibrium for phosphorylase a favors
R state
equilibrium for phosphorylase b favors
T state
What is allosteric negative regulator for glycogen degradation in liver?
Glucose
High glucose in liver will shift equilibrium to
T state (tenseand inactive) of phosphorylase a
Low glucose in liver will shift equilibrium to
R state (relaxed and active) of phoshorylase a
Default state of muscle phosphorylase is:
inactive phosphorylase b form
since glycogen breakdown just needs to be active for muscle contraction and when resting muscle, enzyme is in inactive b form
What are allosteric effectors of glycogen degradation in muscle?
AMP, ATP, glucose phosphate
have low energy with high level of AMP (indicate low energy charge) in muscle:
shift from T to R (active) state of phosphorylase b
high energy charge (high ATP and glucose 6 phosphate in muscle:
shift from R to T state (less active) of phosphorylase b
Key regulatory enzyme in glycogen synthesis?
Glycogen synthase
2 forms of glycogen synthase:
- active nonphosphorylated a form
- inactive phosphorylated b form
Low glucose (glucose 6 phosphate) of glycolysis synthesis shifts
R state to T state (inactive phosphorylated b form)
What is the activator of glycogen synthase?
glucose 6 phosphate and stabilizes R state
High glucose (glucose 6 phosphate) of glycolysis synthesis shifts
T state to R state (more active nonphosphorylated a form)
What two hormones signal need for glycogen breakdown?
Epinephrine and glucagon
Epinephrine and glucagon activate and inhibit what
activate glycogen phosphorylase
inhibit glycogen synthesis
signal need for glycogen breakdown
Insulin results in decrease in _____ and stimulation of _____
glycogen degradation
glycogen synthesis
Insulin hormon activates what enzyme
glycogen synthase
Glycogen synathase and glycogen phosphorylase are controlled by ______ and _______
covalent modification
allosteric control
Protein Phosphatase 1 (PP1) shifts glycogen metabolism from _____ to ________
degradation
synthesis
Protein phosphatase 1 (PPI) reverses effects of
kinases
Protein phosphatase 1 removes:
Removes phosphoryl groups from glycogen synthase b and convert it to active form –> stimulate glycogen synthesis
Removes phosphoryl groups from phosphorylase kinase and phosphorylase a –> inhibit glycogen degradation
